Integrated circuits (IC) play a significant role in the field of modern semiconductor technology. The development of integrated circuits has made possible a modern world with advanced electrical technology. Applications of integrated circuits are so widespread and their significance affects our every day lives from cellular phones, digital televisions, to flash memory chips in cameras. These integrated circuits typically are formed on silicon substrates or wafers, which can include active semiconductor devices with structured processes for a wide range of stacked layers made from different materials, allowing for memory capabilities.
Recently, in modern semiconductor technology, integrated circuits have advanced towards smaller devices with more memory. In the manufacture of semiconductor integrated circuits (IC), typically, dielectric materials such as silicon dioxide (SiO2), silicon nitride (Si3N4) and silicon oxynitride (SiON) have been widely used. However, as technology has progressed, IC device geometry has become smaller, resulting in progressively thinner integrated circuit devices. When typical IC devices approach thicknesses of a few nanometers or less, conventional aforementioned dielectric materials can typically undergo electronic breakdown and can no longer provide the memory storage needed.
To address the aforementioned problems, high dielectric constant materials (high k dielectric materials) have been used in semiconductor chip manufacturing with their potential application in memory devices. Examples of high k materials include aluminum oxide, (Al2O3), hafnium oxide (HfO2), zirconium oxide (ZrO2) and mixtures thereof, and metal silicates such as HfSixOy, ZrSiO4 and mixtures thereof.
Although the aforementioned high-k materials are sought after for their use in IC applications, it is known to those skilled in the art that it can be very difficult to dry etch. High k materials typically are very stable and resistive against most etching reactions (due to their chemical inertness), which has led to their use as etch stop layers and hard mask layers in plasma etching and other materials.
While a typical deposition process desirably generates high k dielectric films on a substrate (for example, a silicon wafer), unwanted reactions can form on these films and other parts of a reaction chamber. Accumulation of these unwanted residues can result in particle shedding, degradations of deposition uniformity and these effects can lead to wafer defects, and the worse, subsequent device failure.
With respect to high dielectric constant materials, aluminum oxide (Al2O3) typically is known to those skilled in the art to have one of the slowest etch rates. Typically, even under powerful plasma conditions, conditions can result in high chuck bias voltage resulting in enhanced ion sputtering and sputter induced etching.
Conventional methods of etching high k dielectric materials, typically involves chlorine (Cl2) gas at a high wafer temperature, and fluorine gas. There have been many disadvantages with these methods. It is well known to those skilled in the art that Cl2 based chemistry aggressively etches polysilicon (poly), resulting in low selectivity to poly. The etched high k dielectric layers can form a residue on the wafer after etching yielding in low capacitive structures or defective wafers. Specifically with respect to aluminum oxide, this represents a great difficulty to etch Al2O3 on top of a thin poly1 layer for flash memory and other related applications. Fluorine has been shown to be typically ineffective in etching high k dielectric materials. Fluorine can typically produce a metal fluoride product that is nonvolatile and thus difficult to remove from the reactor.
A flash memory stack for 55 nm node and beyond consists of poly2/Al2O3(or other high k dielectric material)/poly 1. It is well known to those skilled in the art, that Al2O3 is different from poly in the film stack and difficult to etch. The key for successfully etching high k dielectric materials, such as Al2O3 on top of a thin layer of poly 1 layer of the new flash memory film stack is to find a process which has a reasonable Al2O3 etch rate and a high selectivity to poly silicon.
As those skilled in the art would appreciate, there is a need for methods that can etch high dielectric constant materials. Such methods of etching should preferably not have the undesirable properties of promoting unwanted residues that could make the wafer defective. Still further, there is a need for methods to etch high dielectric constant materials, such as aluminum oxide, that are cost effective, have high selectivity and a reasonably high etch rate.